Print last expression in a Crystal program

eval.cr

require "compiler/crystal/syntax"


def transform_eval(source)
  ast = Crystal::Parser.parse(source)
  unless ast.is_a?(Crystal::Expressions)
    ast = Crystal::Expressions.new([ast])
  end
  exprs = (ast as Crystal::Expressions).expressions

  case exprs.last
  when Crystal::Require, Crystal::Def, Crystal::FunDef,
       Crystal::Macro, Crystal::ClassDef, Crystal::LibDef
  else
    # Wrap last expression
    expr = Crystal::Parser.parse(%[
      x.try { |e| puts "\\n#=> \#{e.inspect}" }
    ]) as Crystal::Call
    expr.obj = exprs[-1]
    exprs[-1] = expr
  end

  ast.to_s
rescue
  source
end


puts transform_eval(ARGV[0])

test.txt

$ crystal build eval.cr

$ ./eval 'require "json"; JSON.parse(%({"a": [1,2,3]}))' | tee >(crystal eval)                                                                                           

require "json"
(JSON.parse("{\"a\": [1,2,3]}")).try do |e|
  puts("
#=> #{e.inspect}")
end

#=> {"a" => [1, 2, 3]}

$ ./eval 'queue = Channel(String).new(5); spawn { 10.times { queue.send "hello" }; queue.close }; Array.new(5) { queue.receive }.join' | tee >(crystal eval)

queue = Channel(String).new(5)
spawn do
  10.times do
    queue.send("hello")
  end
  queue.close
end
(Array.new(5) do
  queue.receive
end).join.try do |e|
  puts("
#=> #{e.inspect}")
end

#=> "hellohellohellohellohello"